The present invention relates to an IC card system and, in particular, an IC card system of such a type that, even if, upon the use of an IC card as a "prepaid" card for instance, data is found to be destroyed owing to a damaged IC chip, etc., data items, such as a "prepaid" balance, recorded in the IC card can be identified by the IC card and the terminal in a self-solving way without using any large-scale on-line system and can be restored with added safety.
A prepaid card, such as a conventional prepaid telephone card, is not safe from the standpoint of security, such as the protection of secret data and prevention of tampering. In the conventional prepaid card system, when data items in the prepaid card are maliciously or inadvertently destroyed by a card owner or any third party, there is no safe countermeasure for restoring data on a "prepaid" balance.
An IC card equipped with an IC version of a data storing/processing circuit is outstandingly superior to other cards from the standpoint of security, such as the protection of secret data and prevention of the tampering of data.
There is a relatively high possibility that, because such an IC chip is embedded in a plastics card, data items in the card will be destroyed, not to mention damage to the IC itself. Further, in the event of the data items being destroyed in the card, it is not possible to identify data, such as a "prepaid" balance. Even if any dispute arises between a card owner and a card issuing person in connection with the "prepaid" balance, there has been no effective solution to such a problem.
There is, therefore, a growing demand for identifying and restoring data items in the IC card system as set out above. An effective measure, therefore, is necessary to readily identify damaged data without using any large-scale on-line system and to prevent any possible misuse upon the re-issuing of an IC card.
It is an object of the present invention to provide an improved IC card system in which final transaction data items, once disturbed by encryption, are recorded in a magnetic or optical data recording unit whereby, when data items in the IC card are destroyed, the recorded data items are read out of the data recording unit to enable the read-out data items to be readily identified for their truth.
Another object of the present invention is to provide an IC card system which, when data items read out of a magnetic or optical data recording unit is proved true, restores the true data items in a new IC card.